Updated `fedora_submit.py` to use `python3`. I uninstalled the
    `python2-fedora` package, installed the `python3-fedora` package
    (and it's automatically-pulled dependencies) on Fedora 28, ran the
    default regressions, and the submission script worked as expected.
    
    I also tweaked `documentation.txt` to be in Markdown format, plus made
    a few minor style changes. The overwhelming majority of the text is
    unchanged and the structure is largely the same. The mapping between
    the original style and the Markdown version is readily apparent when
    the two are viewed side-by-side.